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    Subject[tip:core/rcu] rcu: Fix holdoff for accelerated GPs for last non-dynticked CPU
    Commit-ID:  622ea685f1fafdf84d612440535c84341f0860b8
    Gitweb: http://git.kernel.org/tip/622ea685f1fafdf84d612440535c84341f0860b8
    Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    AuthorDate: Sat, 27 Feb 2010 14:53:07 -0800
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Sun, 28 Feb 2010 09:17:42 +0100

    rcu: Fix holdoff for accelerated GPs for last non-dynticked CPU

    Make the holdoff only happen when the full number of attempts
    have been made.

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: laijs@cn.fujitsu.com
    Cc: dipankar@in.ibm.com
    Cc: mathieu.desnoyers@polymtl.ca
    Cc: josh@joshtriplett.org
    Cc: dvhltc@us.ibm.com
    Cc: niv@us.ibm.com
    Cc: peterz@infradead.org
    Cc: rostedt@goodmis.org
    Cc: Valdis.Kletnieks@vt.edu
    Cc: dhowells@redhat.com
    LKML-Reference: <1267311188-16603-1-git-send-email-paulmck@linux.vnet.ibm.com>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    kernel/rcutree_plugin.h | 8 +++++---
    1 files changed, 5 insertions(+), 3 deletions(-)

    diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
    index 464ad2c..79b53bd 100644
    --- a/kernel/rcutree_plugin.h
    +++ b/kernel/rcutree_plugin.h
    @@ -1010,6 +1010,10 @@ int rcu_needs_cpu(int cpu)
    int c = 0;
    int thatcpu;

    + /* Check for being in the holdoff period. */
    + if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies)
    + return rcu_needs_cpu_quick_check(cpu);
    +
    /* Don't bother unless we are the last non-dyntick-idle CPU. */
    for_each_cpu_not(thatcpu, nohz_cpu_mask)
    if (thatcpu != cpu) {
    @@ -1041,10 +1045,8 @@ int rcu_needs_cpu(int cpu)
    }

    /* If RCU callbacks are still pending, RCU still needs this CPU. */
    - if (c) {
    + if (c)
    raise_softirq(RCU_SOFTIRQ);
    - per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
    - }
    return c;
    }


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